This invention relates to an apparatus for detecting a failure in a solenoid valve having an electrical winding electromagnetically coupled with a plunger.
For example, Japanese Patent Kokai No. 60-40856 discloses a conventional apparatus for detecting a failure in an oil pressure control unit. The conventional apparatus employs an oil pressure sensor provided in an oil conduit connected to the output side of a shift valve. The shift valve is judged to be subject to a failure when the sensed oil pressure is different from the oil pressure to be sensed when the shift valve is operating in order. However, the conventional apparatus requires a number of oil pressure sensors to check all of the shift valves, resulting an expensive and space-consuming failure detecting apparatus.